Unevenness arises in display panels, such as liquid crystal panels and organic electroluminescent (EL) panels, due to inconsistencies in manufacturing processes, and there has been a desire to quantitatively evaluate the extent of such unevenness to judge whether products are non-defective or defective, carry out grading, and so on.
Evaluation based on the amplitude of unevenness (contrast) can be considered as a way to easily make a quantitative evaluation. However, such a method is problematic in that display panels having unevenness that, while having a high amplitude, is not visually bothersome to humans (or cannot be seen at all) are judged to be defective, whereas display panels having unevenness that, while having a low amplitude, is visually bothersome to humans (or simply can be seen) are judged to be non-defective.
Patent Document 1 describes a method in which luminance distribution information of a display panel (display) is obtained, and a contrast image is generated by finding a luminance change amount from the difference between the luminance distribution information and a background luminance and then dividing the luminance change amount by the background luminance. The contrast image is then subjected to a two-dimensional Fourier transform to obtain a two-dimensional Fourier spectrum, after which a convolution power spectrum is found by multiplying the two-dimensional Fourier spectrum by a visual transfer function (a contrast sensitivity function) based on the vision characteristics of humans. Finally, the convolution power spectrum is subjected to a two-dimensional inverse Fourier transform, and luminance unevenness in the display panel is quantitatively evaluated. In consideration of background luminance dependence and screen size dependence, Barten's formula is used as the stated function.